----- Original Message -----
Sent: Thursday, November 24, 2005
10:17 PM
Subject: Re: [PSUBS-MAILIST] Re:
Working Schematic, specifications
Hi, Joe . . .
If I am understanding what I have
learned so far "floodable interior space" is the total displacement of the
air volume that you are trying to submerge.
I've never heard that particular term before.
It seems contradictory. Rather than complicate things by
establishing nomenclature [just for the moment] I'll refer to the
interior dry volume (cabin) as the bubble I have to force
underwater.
A dry cockpit volume of 4 x 4 x 4 will yield 64
cubic ft. or 4100 lb. of buoyancy. Weight includes two occupants at
150 lb. ea. Also include the seats, instruments, dash panels,
batteries, controls, a good book [Busby - at least 35 lb.], a packed lunch
with thermos and a sleeping bag and misc. other items. Obviously, if
you have 4100 lb. of keel ballast in the form of, say, lead, you're going
to the bottom fast. Let's put less lead in the amount of all that
cargo we mentioned above.
Lead + cargo = cockpit bubble. That's
it.
All other materials, say, ply hull,
fibreglass/resin, motors, deck fittings, anchor/chain/rope, skeg, etc.
that will be fully immersed will have an amount of buoyancy depending on
their particular specific gravit
This is the difference between dry
weight and what would be required to submerge to neutral buoyancy. Quite
frankly, I am having trouble determining how to look at it, whether soft
water ballast is "increasing" weight or "decreasing" displacement or
perhaps both?
"Soft tanks" are upside down glasses that you fill
with air at the surface to lift the boat higher out of the water.
Open at the bottom like a glass. Very little inherent pressure
internally. No reason to have much pressure. They still have
to be sturdy.
That figure above is roughly the 30%
ratio to interior volume for a seagoing boat as Carsten had pointed out.
He had also pointed out that high volume soft ballast ratios are not
unheard of as in this example so I am still playing with the
idea.
Take a look at your own boat. Everything other
than your dry cockpit/cabin will be wet. Those areas will be flooded
100%. No mystery. Your hull is for streamlining and lifting
your boat out of the water while surface running.
Where the confusion may be arising is in the hard
tank[s]. At the surface, having lots of hull space to force air into
will lift your boat up high. Those are the soft tanks.
The hard tank [as in "hard-walled" to resist water
pressure] is used to fine-tune your neutral buoyancy. It is NOT open
at the bottom - it's sealed against pressure. Ideally, if this
sealed box is full of air, the sub will not dive - it's too light.
Your cockpit canopy will be awash. If this box is filled 100% with
seawater, your boat will be too heavy - it will sink.
During normal use, if the usual occupants' weight is
known, the weight of Busby's book is known, your cell phone, note pad,
video camera, box lunch and pina colada thermos are all known weights,
THEN you can remove lead to the point where your hard tank will be filled
about half way to achieve neutral buoyancy.
Until then, using these known weights, your canopy
will forever more be doomed to be awash until that hard tank is filled
half way with sea water.
So why is it hard? To keep Boyle's Law out of
your hair. An open [soft] tank will accomplish the same thing as a
hard tank - for the first few feet of depth. Once the air starts to
compress, you'll face every diver's dilemma - keeping neutral
buoyancy.
A hard tank will isolate the ocean pressure from the
contents and the air in this hard tanks will not contract.
A company called Dacor designed a hard tank scuba
pack [back in the eighties, I believe] to get around Boyle. It
wasn't a success. Apparently the pack wasn't strong enough to last
through to full scuba depths and you had to release pressure
mid-dive. Not easy to control. Now, if you build one out of
Al2. There's thought.
If you want to maintain some degree of
scale in a replica you run into these volume and length problems. What
have you worked out for your Typhoon replica "Magical Child?"
Hardy-har. Finally someone else with the same
dilemma!!! These subs were designed around using the entire interior
as dry volume.
Your particular affliction - and mine - is to
maintain the same degree of "look" or authenticity as the original.
It wouldn't look cool if the lines weren't right. You, I
suspect, have an artsy streak running through you. I'd be willing to
bet you'd never be happy with anything but an Italian motorcycle [damn the
electrics]. http://www.motoguzzi-us.com/bikes/v11lemans/index.html
Soo-weet.
[origin of the name Magical Child: http://www.thewellspring.com/cat/adult_books/magical_child.html ]
For Magical Child, I've had to compromise between authenticity [the cool
factor] and the length of my workshop. I truncated Magical Child
until I could squeeze it into my 18 foot shop. A 15 X 2.5 ft. [NOT
the original Typhoon L/B ratio] hull allows tandem seating [not my first
choice] and a 6:1 ratio. Not bad. It'll flow smoothly on the
surface, offer a large deck area for movement, lounging, etc., will be
fairly kind in a seaway [no thanks to its bows], will be hydrodynamic
underwater, and will keep the props in the water during heavy
seas.
It'll also be aesthetically
pleasing.
Dans words keep ringing in my ears
though and I believe it was you who suggested a "proof of concept" boat. I
am seriously looking at downsizing even further to a two man craft or
smaller.
Put a canopy on it, compensate the cabin and Bob's
your uncle. Proof-of-concept still has to be fun. I have not
the resources to do this solely as an intellectual exercise (hmmm . .
. that didn't come out right). It HAS to be fun as soon as the
thing hits the water.
The S-boats at 219' by 20.6' could be
scaled to roughly 1/10 and come to about 22' x 3'. A single cylinder
diesel/electric would be damn cute!
A different L/B ratio would simply make a fatter
boat. Decent lines could still be
maintained. I enjoy inserting a jpg of a sub drawing into Word, then
using the image markers to expand or contract the image as I see
fit. Hold a ruler up to the screen or use Word's built in rulers and
you can get INSTANT visual results with ratio changes.
Do it with both the elevation and plan views.
It's a scream. BTW, if the technique appeals to you, mess with the
sectional views, too. Print out a copy of the proportions you like,
white-out the yucky parts, draw in your own canopy design, scan it back in
to the puter, then play with THAT jpg in Word.
A word on modeling: I've bought several well
proportioned human figures so I could work with them during the modeling
sessions.
http://www.psubs.org/pic/typhoon.html
This link shows one of my human figures. Obviously, the gentleman in
the picture is not in proportion to the hull he's sitting in. It was
for roughing out. I've since bought three more Typhoon hulls of
different scales to play with as well as several other human
figurines/dolls.
The Magical Child model I'll be building
will be thirty inches long because the figure I've chosen is twelve inches
tall. His arms, legs and torso all bend at the right place and
are anatomically well proportioned (my smart-ass 13 year old
daughter, looking over my shoulder, wants to know if he has a
penis) Same boat building techniques as the final build:
glass-over-ply.
Warm regards,
Rick
Vancouver